1. Technical Background of the Invention
Telemetry, in a simplified definition, is the process of sensing data and then transmitting this data to a remote location, usually by a wireless means such as radio. Such devices can be used in applications ranging from industrial process monitoring, environmental/pollution sensing, fire and security alarms, emergency operations, equipment condition monitoring and diagnostics, automotive/vehicular controls, building energy monitoring and control systems, medical/veterinary instrumentation, and in military/battlefield sensing tasks. These remote devices usually perform additional functions as needed, such as conditioning, averaging, or filtering the data or storing it prior to transmission. Currently, these remote transmitter (or transceiver) devices are typically circuit-board based, multi-component assemblies constructed from several independently manufactured chip units. Even in relatively simple transmitter devices, many different functions must be accomplished by units or subsets of the circuitry carried by the devices. In a telemetry device for collecting and transmitting sensor data such as temperature, for example, there are required multiple circuit functions, typically including: a data-acquisition or measurement device in the form of the temperature sensor to detect temperature and provide an analog signal indicative of the sensed temperature; a converter to convert analog data to a digital format; a memory for storing the data; mixing devices to modulate the data onto a carrier such as a radio-frequency wave; and a transmitter. Other types of sensing circuits or functions useful for such applications include optical sensors, flow sensors, humidity sensors, chemical sensors, biochemical sensors, electrical current sensors, electrical voltage sensors, magnetic-field sensors, electric-field sensors, mechanical force sensors, acceleration sensors, velocity sensors, displacement sensors, position sensors, vibration sensors, acoustic sensors, radiation sensors, electrical-charge sensors, viscosity sensors, density sensors, electrical resistance sensors, electrical impedance sensors, electrical capacitance sensors, electrical inductance sensors and mechanical pressure sensors. These sensor types may be primarily electrical in nature (e.g., bridge circuits), electromechanical (“MEMS”) with electronic or piezoelectric readouts, optical (e.g., a photodiode or phototransistor), a purely piezoelectric, piezoresisitive, or magnetoresistive transducer device, or some combination thereof. Ideally, these sensor devices would be integrated into the same integrated-circuit chip, although in practical implementations this is sometimes not currently feasible due to incompatibilities between the processes used to manufacture the sensors (such as MEMS devices) and the standard silicon electronic circuits, particularly modem mixed-signal (analog plus digital) CMOS [complementary metal-oxide semiconductor], as used in the prototypical telesensor chip described herein. In the cases where the sensor must be separate from the main telesensor system chip, the main chip can still provide amplification, filtering, and other signal conditioning for the signals from off-chip sensors feeding the external input(s) of the main device.
The overall functionality of these telemetry devices is severely hampered by the size and the complicated architecture and inter-chip connections inherent in a multi-chip device. The relatively large size of these devices markedly limits the useful locations thereof. In addition, these devices have relatively high power requirements. It is known in the art, for example, that the chip-to-chip signal transmission in such devices alone creates a high power demand in addition to the power needed to operate or drive each of the individual subcomponents on each chip. An additional constraint involves overall power consumption; since many remotely located telemetry systems are battery-operated or powered by low-energy sources such as solar cells, it is vital that the system perform its measurement and reporting tasks with as little average power as possible. Further, since most small power sources are significantly limited in their ability to provide large peak current levels, it is also important that the device control its maximum transient power requirements as well.
Current technology makes attempting to decrease the size and power requirements of telemetry devices, such as by placing all of the system subcomponents on a single chip, difficult or impractical for multiple reasons.
The operations of these different units, and operations incident to the function of the units, usually require or at least reference a timing or clock signal. As is well known in the art, clock signals are used for such operations as controlling the timing of a switch between a high logic state (“on”) and a low logic state (“off”) for a particular unit, for controlling the placement of digital bits within a transmitted stream, and other functions where actions must be coordinated. In a digital transmitter device, some of the required parameters are the frequency of the radio wave (RF) carrier, the baud (data-transmission bit) rate, the data-burst timing, and the data interface rates (e.g., the input speed of serial data). Each of these operations, among others, require a frequency reference source, or clock, for reference and control. Clock signals can be generated by crystal oscillators, SAW (surface acoustic wave) devices, and other oscillation sources are known to the art.
In a data acquisition system, such as a data-acquisition and transmission telemetry device, additional functions are executed. These include conversion of acquired data from analog to digital form where necessary, the writing to and reading from storage or memory of such data, and the provision of instructions creating and controlling the desired cycle of operation. These functions also require or use as a reference a clock signal.
It remains the current practice in designing and creating transmitters and telemetry devices to use separate oscillators, such as the crystals referenced above, to provide the oscillation signal for one, or only a few, clocks, or frequency-reference sources, for separate units and/or functions. Setting center frequencies for RF carriers, determining channel step sizes, and controlling embedded processors and controllers are some examples of operations that almost invariably are controlled by separate clocks. In addition, any other specialized functions or devices incorporated in a digital telemetry device will be provided with additional, separate clocks, even where use is made of frequency synthesis, that is, the multiplication or division of a single clock frequency to provide more than one clock reference.
Even the simplest telemetry device in the art today therefore has several relatively unrelated clocks and thus several relatively unrelated (“asynchronous”) frequencies in the circuits. The frequencies interfere with each, creating “beats” which can in turn contribute more interference. “Beats”, a form of interference, are periodic variations resulting from the superposition of waves having different frequencies and often occur in devices using multiple functional clock signals. The more complicated the device, the more functional clocks are needed, and thus the more complicated and noisy the interference becomes. Especially as devices become both more complicated and smaller, further problems are caused by the cross-coupling of clock signals through capacitive or radiating means. This is of particular concern when the cross-coupling occurs in low-level signal units and units such as synthesizer loop-control lines and modulation signal wiring. More specifically, both complex and small single-chip devices tend to be implemented in modem, very small-geometry monolithic fabrication processes. The extreme proximity of the various signal-transmission lines on the tiny substrates used for single-chip devices only exacerbates the problems of capacitive, inductive and radiative coupling of the multiple unrelated high-speed RF-type clock signals onboard the chip. Interference imposed on these units can mask or interfere with data signals and even create spurious or faulty RF transmissions.
The use of separate clocks is also inherently problematic for other reasons. Having several clocks requires additional circuitry to generate the clock signals, takes up room that could be used for other devices, and is more expensive in terms of both design and manufacture. These problems increase proportionately as techniques improve to reduce the size while increasing the utility of telemetry devices. These problems are markedly exacerbated when the device incorporates on-chip receiver circuitry, either RF or optical, for controlling device parameters or operational functions.
Multiple clock signals cause problems outside the device as well. The more complicated the telemetry transmitter is, the more complicated the receiver must be. The use of multiple clock sources on the transmitter can cause noise that must be internally filtered within the chip. Wireless spread-spectrum transmissions are often embedded in Gaussian (random) channel noise, and spurious transmitted noise components further hinder system performance. Also, receiver acquisition and lock-up times will be longer than optimum (if only to ensure that the lock-up is correct despite the signal's embedded noise) and will thereby reduce the data throughput of the RF link. In addition, a noisier system typically requires higher transmitter and receiver power to ensure that the data signals of interest can be detected above the normal levels of RF channel noise. Finally, high levels of internally generated noise or spurious components in the transmitted signals can ultimately limit the minimum data error rates achievable by the overall telemetry system.
Current construction of these devices also recognizes problems associated with the transmitter. The transmitter typically requires substantially more power than the other sub-units of the telemetry device, and continuous transmission constitutes a significant portion of the total power requirement for these devices. When the transmitter is housed in close proximity to the sensing unit of the device, the strong RF signal produced interferes with the sensor's ability to acquire data, limiting the device's overall utility and sensitivity. Similar types of interference also affect adversely RF, optical, or other types of RF receiving circuitry which also may be present within the device. Further, the heat generated by the on-chip transmitter stages can also adversely affect other, temperature-sensitive parts of the circuitry; in the version of the instant invention which includes an on-chip temperature sensor, its readings will be shifted upward by the transmitter heating, thus causing errors in measuring the ambient temperature.
2. Description of Related Art
A review of several patents in the existing art confirms the deficiency of current designs in failing to provide a fully synchronous RF transmitting architecture capable of being manufactured as a single-chip device. For example, U.S. Pat. No. 4,916,643, issued Apr. 10, 1990 to Ziegler et al., discloses a remote temperature-sensing and signal-multiplexing scheme that utilizes a combination of a primary pulse-interval modulation and a secondary pulse-amplitude or pulse-width modulation transmission technique. The application is to combine several sensor-data channels over existing wire busses via time multiplexing; the secondary pulse-amplitude and/or pulse-width modulations simply represent the analog values of the respective sensor data streams. The system does not employ any type of RF or spread-spectrum data transmission and does not in any way embody an RF data link.
U.S. Pat. No. 3,978,471, issued Aug. 31, 1976 to Kelly, discloses a drift-compensated digital thermometer circuit which employs a temperature-sensitive resistor in a standard analog bridge circuit, which in turn is read out by a common dual-slope analog-to-digital (A/D) converter. The local voltage reference source is used to drive the A/D on alternate cycles between the temperature conversions, and thus compensate for any drifts in the reference voltage. This feature obviates the need for a precision, highly stable reference voltage source in the system. This patent has no provisions for data transmission or spread-spectrum coding; thus it fails to address the subject areas of the instant application.
U.S. Pat. No. 3,972,237, issued Aug. 3, 1976 to Turner, discloses an electronic thermometer system consisting of: a thermistor to measure the desired point temperature; front-end analog pre-amplifier; a voltage-to-frequency converter which generates digital output pulses at a rate determined by the magnitude of the analog input voltage from the temperature measurement; and a counter to accumulate the pulses in a given time interval and display the result digitally. As with the '471 patent above, this device has no means of transmitting its data to a remote location and lacks most of the other attributes of the present invention.
U.S. Pat. No. 4,644,481, issued Feb. 17, 1987 to Wada, describes another electronic thermometer system, consisting of: an oscillator whose frequency is determined by a temperature-sensitive resistor; a counter to accumulate the oscillator output pulses during a predetermined time interval; a timer to generate said interval; a memory to store said temperature data; and a calculator circuit to compute changes in the temperature data and track trends therein. As in the previous patents, no means of transmitting data or developing spread-spectrum modulation is included; further, no clock-synchronization circuitry is evident.
U.S. Pat. No. 5,169,234, issued Dec. 8, 1992 to Bohm, discloses an infrared (IR) temperature sensor with an non-contacting infrared-emissivity measurement device, coupled to a local temperature-compensating element; an analog front-end amplifier; a voltage-to-frequency (V/F) type of A/D converter to digitize the IR sensor reading; a second A/D converter to digitize the local reference-junction device to compensate for the local temperature of the IR detector; a microprocessor to combine the various readings and apply nonlinear corrections as needed to the IR emission measurement to provide an accurate temperature therefrom; a user interface and display; and coupling means to interface to an external two-wire bus. Although this device incorporates several of the data-acquisition features of the instant system, it nevertheless is greatly diverse for the following reasons: it lacks the intrinsic RF transmitting and spread-spectrum encoding functions; it is a multi-component (board-level) system rather than a single chip; it contains a general-purpose microprocessor rather than a customized digital state-machine controller; it lacks the synchronous inter-coordination between data-acquisition and transmission functions; and it consumes far more power than the present invention.
U.S. Pat. No. 5,326,173, issued Jul. 5, 1994 to Evans et al., discloses a technique plus apparatus for improved accuracy of optical IR pyrometry (non-contacting emissivity measurements). The accuracy in remote measurement of temperatures of a specific surface is improved over standard IR techniques by mounting the IR sensor in an integrating cavity and then exposing the target to IR radiation from two or more distinct sources (ideally but not necessarily at different wavelengths). The multiple beams reflect from the target surface at different angles; measurements of the multiple reflected signals can compensate for anisotropy of the target surface and can thus separate the reflected and truly temperature-related emitted components at the detector(s). Although the method is a clear improvement in the remote IR pyrometry art, it does not relate to the instant device, which incorporates a contact-type thermal sensor only.
U.S. Pat. No. 5,735,604, issued Apr. 7, 1998 to Ewals et al. discloses a novel method and apparatus for the contactless determination of the temperature of an object or at least part of an object, generally applied in equipment monitoring to measuring the temperature of a heated roller or endless belt, as in image copying machines and printers. The sensor unit is placed near the object to be measured and consists of two plates, each of which is equipped with a temperature sensor. A control unit takes the two plate-temperature signals and via a predictive Kalman digital filter estimates the temperature of the target object. The estimation process is achieved by utilizing both commomalities and differences in the two plate temperature trends to mathematically model the thermodynamic relationships between the target and the two plates. The models are then used to infer the temperature of the target object. No data formatting or transmission circuitry whatever is disclosed. Although a useful development in the general thermometry art, this patent has no specific bearing on the instant application.
U.S. Pat. No. 5,795,068, issued Aug. 18, 1998 to Conn, Jr., discloses a method for measuring localized operating temperatures and voltages on an integrated-circuit (IC) chip. The device includes a “ring”-type logic-gate oscillator circuit that varies with temperature and/or applied voltage. The frequency of the oscillator is then determined for a number of temperatures to establish a known frequency-versus-temperature (or voltage) response characteristic. A second, identical oscillator circuit is included on the chip. The characteristic of the first oscillator is then used to back-calculate the temperature and/or voltage of the second circuit. The basic monolithic temperature-measuring circuits are already well known in the art. Further, no specific means of telemetering the data off-chip is disclosed. The dual-oscillator technique is useful for detailed production testing of large numbers of IC logic chips, but has no overlap with the instant application.
U.S. Pat. No. 5,892,448, issued Apr. 6, 1999 to Fujikawa et al. discloses an electronic clinical thermometer unit consisting of: a thermal-sensing oscillator; a reference oscillator for control timing; a counter to store the temperature-related frequency value; memory to store successive measurements over a predetermined period; a rate detector circuit to assess if the reading is not sufficiently stable for display; a hold circuit to latch the highest reading in a sequence; and a digital visual temperature display. The logic filters the sensor readings to assure that the thermometer has adequately tight and stable contact with the patient's body to generate a clinically accurate reading. This oscillator-type thermometer operates in a different manner to the analog sensors onboard the device of the instant invention; further, the self-contained unit in '448 has no provisions for formatting, encoding, or wireless telemetry of the temperature data to an external receiver.
U.S. Pat. No. 5,914,980, issued Jun. 22, 1999 to Yokota et al. disclose a wireless spread-spectrum communication system optimized for use in batteryless “smart” cards and complementary reader/writer units to read, transfer, and store data on the card for commercial and financial applications. Spread-spectrum wireless signals are used to provide improved robustness and data reliability in typical transactions, as well as to power the small card through an onboard RF pickup coil. The fixed reader/writer unit contains a low-power transmitter operating in the vicinity of 200 kHz into a coil antenna to couple the required RF energy into the card. The single-chip card circuitry, via a standard phase-locked loop (PLL), multiplies this power-signal frequency up to roughly 4 MHz to operate onboard microprocessor, logic, memory, and data-transmitter clocks. The return spread-spectrum data link also operates at 4 MHz to send stored information back to the reader/power unit. Although several elements of the instant invention are utilized in the system of '980, the application is profoundly different. In '980, there are no sensors, no digitizer functions, and no data-acquisition or processing features. Further, the '980 devices have only a small number of possible spreading codes and no real power-management capability (i.e., programmable power-cycle times). No attempt has been made optimize the RF link data rate, spreading rate, burst times relative to standard RF data channels (i.e., with typical impairments such as interference, noise, multipath) due to the stated close proximity of the two units (card and reader) in their intended application. The instant device, in contrast, is designed to operate at much higher frequencies useful for longer range communications (typically tens of meters to kilometers).
Finally, U.S. Pat. No. 5,838,741, issued Nov. 17, 1998 to Edgar Callaway, Jr. et al. discloses a scheme that ensures that digital data in an RF receiver is transferred to downstream stages only at times which will have minimal impact on the front-end and other more sensitive parts of the circuit. The scheme is generally applicable to miniature units and particularly relevant to single-chip (monolithic) devices. The salient goal is to minimize on-chip data transfers (with their inherent noise) during any critical signal-sampling instants, delaying them to less sensitive times. The system controller can be configured to insert an optimum delay into the various subsystem control lines to avoid logic transitions at noise-critical times for the various circuits. Although the techniques therein are useful for the manufacture of receiver hardware, they only deal with noise generated internal to a receiver and do not in any way address noise and degradations affecting the output signal from a wireless (RF) transmitter. Further, they do not recognize the benefits of completely synchronous (and thus fully deterministic) system operation, but rather only deal with the judicious insertion of logic delays to minimize the undesired time-sensitive signal crosstalk and other interactions.
Therefore, there abides a need in the art for devices and methods that overcome the problems currently being experienced and capitalize on the advantages inherent in a single chip telemetry device.